After spending a little time riding our KFX90 in stock trim, we wanted to extract a little more power from the green machine. Our main goal was to improve the torque for hill climbs and sandy trails without spending a fortune in the process. To do this, we ordered up a PowerCore 4 system from the Flying Machine Factory (FMF).

FMF has been making ATV exhaust systems for well over 20 years now. Recently, they dropped all of their prices, so the system for our Kawasaki retailed for a reasonable $160. When we searched other companies for comparable systems, we couldn’t find anything even close to the $200 mark. This FMF product is a one-piece spark-arrested system. The entire system is made from stainless steel, with the exception of the aluminum end cap. Total weight is under 5 pounds compared to the one-piece stocker, which weighs over 8 pounds.

The $159 one-piece FMF exhaust system was a snap to install. It took longer to remove and replace the right-side floorboard on this KFX90 than it did to mount the exhaust system.
The $159 one-piece FMF exhaust system was a snap to install. It took longer to remove and replace the right-side floorboard on this KFX90 than it did to mount the exhaust system.

Installation time for the FMF product took under an hour from start to finish. We had to remove the right-side floorboard to gain access to the stock system. FMF supplies easy-to-read instructions, and they even provide a list of tools required for the task. The product fit great.

Before we went for a test ride, we took sound readings on both the stock system and FMF product. At idle, both tests gave a 82 dB reading. At 3500 rpm, the FMF system had a noticeable increase in sound levels with a 92 dB reading compared to 88 dB for the stocker. The sweet-sounding FMF system is still well under the limits you may have to adhere to for any race or ride area.

Adding to our FMF upgrade, we installed a $20 air filter from Twin Air ([800] 749-2890, The one-piece design is easier to clean than the stock unit, and it traps dirt just as well.

On startup, you can easily tell throttle response is improved with the FMF system. The sound level is not annoying, and it gives the Kawasaki a racier feel. To gauge bottom-end power, we set a start mark, as well as a finish line, on an uphill trail to test the FMF pipe against the stocker. The FMF product finished three seconds quicker and was going 22 mph when it crossed the finish line; the stocker had only reached 20 mph. On its way downhill, the FMF-equipped mini reached a top speed (still not hitting the rev limiter) of 28 mph, while the stock system could only muster 25 mph.

Kawasaki’s KFX90 is competitive with the other currently available minis. Plus, they are easy to make better with quality parts from companies like FMF Racing. If we make this machine any faster, we will have to look into suspension upgrades for sure.
Those performance differences not only helped in drag races but on tight trails too. Our pint-sized test rider could squirt through and over obstacles noticeably quicker. In the sandy sections of our test track, we could navigate the trails easier and was bogged down and stuck much less than before.

After installing the FMF complete exhaust system on our KFX90, our goals for more torque and better performance were easily met. Our mini is more fun to ride and sounds much better than when it was stock. We had hoped to not break the bank getting to our goals, and with FMF’s recent price reduction, we did so and then some. FMF has complete and slip-on exhaust systems for most sport and utility ATVs to improve performance, and they are priced right these days. Contact them at (310) 631-4FMF or

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